1. Field of the Invention
The present invention relates to an ink jet apparatus that circulates ink through an ink jet head and ejects ink from nozzles of the ink jet head, and a control method thereof.
2. Description of the Related Art
Conventionally, the ink jet apparatus that circulates ink through an ink jet head and ejects ink from nozzles of the ink jet head has been known. For example, there are the ink jet apparatuses described in US 2002/0118256A1 and US 2005/0007399A1.
It is important for such an ink jet apparatus that the pressure of ink at the neighborhood of nozzle openings of the ink jet head should be always maintained at a constant level.
The ink jet apparatus described in US 2002/0118256A1 has a problem that although the pressure of ink at the neighborhood of nozzle openings largely depends on channel resistance of the pipeline between an ink tank and the ink jet head, the pressure of ink at the neighborhood of the nozzle openings is not constant because no consideration is given to the channel resistance.
On the one hand, the ink jet apparatus described in US 2005/0007399A1 comprises a pressure reference. Liquid level control is difficult for the pressure reference. Furthermore, there is a problem that since a large quantity of ink should be supplied to the pressure reference by a pump, the pump consumes much energy to operate.
An object of the present invention is to provide an ink jet apparatus that can always maintain the pressure of ink at the neighborhood of nozzle openings at an appropriate pressure without requiring complicated control and without involving considerable energy consumption.